Reversible resistivity-switching (RRS) materials such as metal oxides may be used as storage elements in memory arrays. For example, U.S. Pat. No. 7,812,404, filed May 9, 2005 and titled “NON-VOLATILE MEMORY CELL COMPRISING A DIODE AND A RESISTANCE-SWITCHING MATERIAL,” which is hereby incorporated by reference herein in its entirety, describes a rewriteable non-volatile memory cell that includes a diode coupled in series with an RRS material such as a metal oxide or metal nitride.
However, fabricating memory devices from metal oxide rewriteable resistivity-switching materials with desirable switching characteristics is difficult; and improved memory devices that employ metal oxide resistivity-switching materials are desirable.